The important role of local dispersed phase hold-ups for the calculation of three-phase bubble columns

A computational fluid dynamics model is used to calculate a three-phase (air–water–solid particles) flow in a bubble column. The calculation of multi-phase flows is significantly influenced by the formulation of the inter-phase drag and the modelling of the turbulence. Both are influenced by the dispersed phases. The kk–εε turbulence model extended with terms accounting for the bubble-induced turbulence is used to calculate the eddy viscosity of the liquid phase. Bubble–bubble and particle–particle interactions are considered as well as a direct momentum transfer between the two dispersed phases bubbles and solid particles. The local volume fractions of the dispersed phases are considered for the calculation of the drag coefficients between the dispersed phases and the continuous phase. Measured local gas and solid hold-ups as well as measured liquid velocities are compared with the corresponding calculated results. The measured and the calculated results show good agreement.